1. Field of the Invention
The invention relates to a single wafer type substrate cleaning method and a single wafer type substrate cleaning apparatus, more particularly to a single wafer type wet cleaning technique or system for applying a cleaning treatment to substrates such as semiconductor wafers one by one during the fabrication process as well as certain devices such as electronic parts and the like.
2. Prior Art
A so-called batch type wet cleaning system has been the principal method of cleaning substrates such as semiconductor wafers (hereinafter referred to simply as xe2x80x9cWafersxe2x80x9d), whereby wafers stored in a carrier cassette are immersed in sequence in wet bench type cleaning baths arranged in series, or wafers are directly immersed in the cleaning baths through a transfer unit without being stored in a carrier cassette. However, semiconductor devices have reached the sub micron age, in that they are now micro-fabricated and highly integrated, such that the face of wafers has recently required a very high degree of cleaning density, and wafers which are not stored in a cassette have to be wet-cleaned individually in a sealed cleaning housing. To this end, a so-called single wafer type wet cleaning system intended to meet the requirement of a higher cleaning density has been developed.
Under the single wafer type wet cleaning system, wafers can be cleaned with the use of a simple and compact cleaning system in a relatively clean atmosphere where particles and the like do not settle or remain on the face of the wafer. This system is therefore practical to use for small scale production.
Under the single wafer type cleaning system, wafers can be cleaned by the application of various chemical fluids on the face of wafers in a predetermined order, and finally dried by a spin drying treatment whereby the wafers are rotated at high speed. However, there are cases where oxygen remains in the sealed cleaning housing during the drying treatment phase depending on the kind of chemical fluid used, such that the face of a wafer is prone to oxidization. Accordingly, improvement of the system is desirable.
The present invention has been made in view of the aforementioned conventional problems, and it is the object of the invention to provide a single wafer type cleaning method capable of effectively preventing the face of the wafer from becoming oxidized while optimizing the benefits of the single wafer type wet cleaning system for individually cleaning wafers which are not stored in a cassette in a sealed cleaning housing.
Another object of the invention is to provide a single wafer type cleaning apparatus having the means of carrying out the single wafer type cleaning method set forth above as the first object of the invention.
To achieve these objectives, the proposed method comprises the application of a spin drying treatment to the wafer when the wafer is supported and rotated at high speed while an inert gas for preventing oxidation is supplied to the face of the wafer during the drying process, and the inert gas supplied to the face of the wafer is such that the amount supplied at the outer region of the wafer is larger than that supplied at the center thereof.
In the preferred embodiment, a sealed drying space is intended to be formed at the outer region of the face of the wafer and inert gas is supplied to the inside of the sealed drying space, wherein the inert gas is a nitrogen gas (hereinafter referred to as xe2x80x9cN2 gasxe2x80x9d).
Further, the single wafer type cleaning apparatus of the invention which is deemed suitable for carrying out the foregoing cleaning method comprises (1) a wafer rotary means for supporting and rotating a single wafer in a horizontal position in the cleaning housing; (2) a cleaning chamber provided at the outer region of the wafer rotary means for the purpose of forming a cleaning treatment space for the wafer which is rotatably supported by the wafer rotary means; (3) a chemical fluid supply means for supplying cleaning fluid to the face of the wafer which is rotatably supported by the wafer rotary means; (4) and an inert gas supply means for supplying N2 gas intended to prevent oxidation on the face of the wafer which is rotatably supported by the wafer rotary means, wherein the supply port of the inert gas supply means is designed in such a manner that the amount of N2 gas supplied to the outer region of the face of the wafer is larger than that at the center thereof.
In the preferred embodiment, the inert gas supply means has a gas injection section consisting of a circular cover body intended to form a sealed drying space at the outer region of the face of the wafer which is rotatably supported by the wafer rotary means while cooperating with the cleaning chamber, wherein the gas injection section comprises a flat hollow body which communicates with an inert gas supply source at the inside thereof and the supply port at the plane bottom portion.
The supply port of the gas injection section comprises a plurality of injection openings which are disposed radially and arranged concentrically with the face of the wafer, which is rotatably supported by the wafer rotary means, and these injection openings are designed in such a manner that the sum of the areas of the injection openings at the outer region of the face of the wafer is larger than that at the center thereof as the injection openings direct toward the outer region of the wafer.
Further, a baffle plate is interposed in the hollow section of the gas injection section to prevent the inert gas from directly flowing to the center of the supply port of the inert gas.
Under the single wafer type cleaning system of the invention, the face of the wafer is cleaned by employing various chemical fluids in the sealed cleaning housing in a predetermined order, and finally the wafer is dried through a spin drying treatment while the wafer is rotated at high speed, in which case, oxygen will likely remain in the sealed cleaning chamber during the drying process depending on the kind of chemical fluid(s) used, resulting in oxidation on the face of the wafer.
To address the foregoing problem, the invention proposes to provide a spin drying treatment to the wafer which is supported and rotated by the wafer rotary means at high speed while being supplied with N2 gas for preventing oxidation on the face of the wafer.
The degree of oxidation on the wafer depends on the concentration of oxygen in the circum-ambient atmosphere on the face of the wafer, and it has been found, as a result of research and tests conducted by the inventors, that concentration of oxygen in the circum-ambient atmosphere on the face of the wafer is higher at the outer peripheral portion of the face of the wafer than that at the center thereof in an ordinary state.
It is thus necessary to make the concentration of oxygen at the outer peripheral portion of the face of the wafer to become zero (0) or close to zero (0) so as to prevent oxidation on the wafer, and to achieve this, the cleaning housing should be purged by supplying N2 gas to the inside thereof. This however requires a considerable volume of N2 gas which would increase running costs and is therefore uneconomical.
According to the invention, the amount of N2 gas to be supplied to the face of the wafer must be such that the amount supplied to the outer peripheral portion of the wafer is larger than that at the center thereof so that concentration of oxygen is allowed to become zero (0) or close to zero (0) while reducing the usage of N2 gas as much as possible in order to prevent oxidation on the face of the wafer.
Described more in detail, the drying process of the single wafer type cleaning system for individually cleaning wafers which are not stored in a cassette in the sealed cleaning housing, entails the support and rotation of the wafer at high speed by the wafer rotary means, thereby applying a spin drying treatment to the wafer while N2 gas for preventing oxidation is supplied to the face of the wafer, and the amount of inert gas supplied to the face of the wafer is such that the amount of inert gas supplied to the outer peripheral portion of the wafer is larger than that at the center thereof. Accordingly, it is possible to improve and enhance the usefulness of the single wafer type cleaning system by providing a method of effectively preventing oxidation on the face of the wafer.
That is, under the single wafer type cleaning system, the wafer is cleaned by the introduction of various chemical fluids in the sealed cleaning housing in a predetermined order, and finally dried through a spin drying treatment while the wafer is rotated at high speed, and simultaneously supplying an N2 gas for preventing oxidation on the wafer. The degree of oxidation that develops on the wafer depends on the concentration of oxygen in the circum-ambient atmosphere on the face of the wafer.
According to the invention therefore, if the amount of N2 gas supplied to the face of the wafer is such that the amount of N2 gas supplied to the outer peripheral portion of the wafer is larger than that at the center thereof, the concentration of oxygen is substantially reduced to zero (0) or close to zero (0) while the usage of N2 gas is decreased as much as possible, thereby preventing oxidation on the face of the wafer.